1. Field of the Invention
The invention relates to data encryption and, more particularly, to a method and system for accelerated decryption of cryptographically protected user data units, and more particularly for the accelerated decryption of hybrid encrypted data.
2. Description of the Related Art
When transporting data from a transmitter to a receiver over a transmission channel, these data are in many cases transmitted in encrypted form to prevent unauthorized third party access to the data. Various encryption methods are known, in particular asymmetrical and symmetrical encryption methods. In a conventional hybrid encryption method, an asymmetrical encryption is combined with a symmetrical encryption. In this case, a generated session key is firstly asymmetrically encrypted using an asymmetrical encryption method, and buffered. Using a symmetrical encryption method, the user data that is actually to be transmitted is then encrypted using the generated unencrypted session key and following buffering is transported over the transmission channel to a receiver. Decryption occurs accordingly on the part of the receiver. The use of a hybrid encryption method means that, firstly, the user data are encrypted using an asymmetrical encryption method, where this allows asymmetrical key management, and, secondly, the high performance and the low demands on the computing power for encryption and decryption of the user data, due to the symmetrical encryption method used, are utilized. The asymmetrical key management uses key pairs which consist of a public key for encryption and a private key for decryption. Owing to the asymmetrical key management the public key, which is used in the asymmetrical encryption method, does not need to be kept secret. The use of the symmetrical encryption and decryption method for the user data leads to increased data rates in comparison to asymmetrical encryption methods with a comparable security level of the key lengths used.
In conventional hybrid encryption methods, the public key portion of the hybrid encryption method represents a performance bottleneck in many practical applications. This applies in particular in the case of software implementations of cryptographic methods, such as in the case of embedded systems, microcontrollers and smart cards. For this reason in conventional systems, which use hybrid encryption methods, special hardware, such as long-number arithmetic logic units, crypto processors or hardware multipliers, is used in many cases to accelerate the public key calculations or asymmetrical encryption and decryption. The public key operations or calculation steps performed during the course of asymmetrical encryption and decryption are complex and require high computing power and are time consuming.